1. Field of the Invention
This invention relates to the production of laminated glazings and particularly the assembly of stacked constituent elements of a laminated glazing by calendering, i.e. by passage of said stacked elements between two series of pressing rollers, as well as the calender equipped with such rollers.
2. Related Art
The calenders known for this type of assembly generally are equipped with two series of rollers: (1) a series of lower rollers placed beside one another, their positions being adjustable independently of one another so as to obtain a precurve corresponding to the desired crosswise curve which generally is the average curve of the glazing, and (2) a series of upper rollers placed approximately in the same way. The two series of rollers also generally are mounted on a mobile frame able to pivot around a horizontal pin, so that the rollers remain perpendicular to the glazing during the entire assembly operation.
The mounting of rollers on the frame is carried out according to the type of calenders used, e.g., they may be fixed directly on the frame or mounted thereon via a cylinder.
The drive of the glazing during the calendering operation is provided by driving rollers which generally comprise one or more of the lower rollers. The drive of the driving rollers is provided by a driving unit including a geared motor mounted at the end of the pivot pin of the mobile frame. The drive from the motor is transmitted by a chain, either to a shaft extending over the entire width of the mobile frame and mounted on this frame in stationary position, or to a unit of splined shafts and universal joints which enable it to adapt to variations in height and inclination existing between the different driving rollers. From the shaft or the shaft unit, the movement is transmitted by other chains to the driving rollers.
When the driving rollers are mounted directly on the pivoted frame, variations in height and inclination between the various driving rollers stem only from the precurve given to the units of pressing rollers. When the driving rollers are mounted via pneumatic cylinders on the pivoted frame, the drive shaft consisting of a unit of shafts should also follow the movements in height transmitted by the driving rollers, due to their mounting on cylinders, as the glazing passes in the calender.
This system operates well when the glazings are slightly curved. But for the glazings with more accentuated and/or more complex curves, for example for glazings of complex shape, this system brings about rigidities and variations of rotation rate of the driving rollers relative to one another because the unit of drive shafts resists variations in height which are imposed and because the universal joints gradually are brought to work at the limits of their angular travel.
This system exhibits another drawback. The necessity of inserting a universal joint in the unit of drive shafts on both sides of a driving roller does not allow two driving rollers to be brought together side by side. Considering the near necessity of inserting in addition a splined shaft element, it therefore is necessary, in order to have a substantially continuous pressing bed, to insert at a minimum two idle rollers between each two driving rollers, which is contradictory to the criteria imposed for a good operation of the calender which requires that a driving roller should always be positioned at the tip of the glazing to make possible its entry in the calender.
This arrangement is not very awkward then assembling slightly curved glazings of approximately trapezoidal shape, whose front tip almost always presents itself at the same location of the series of rollers. On the other hand, in the case of glazings which are more curved and of greater dimensions, it is necessary to increase the number of driving rollers and it is useful to place several of them side by side over at least one part of the series of pressing rollers.